1. Field of the Invention
This invention relates to a computer type electronic flash device arranged to automatically control the quantity of light of a flash according to a distance to an object to be photographed and more particularly to an electronic flash device in which a light level is controlled by generating preliminary flash before main flashing is produced. For simplicity this computer type electronic flash device is referred to herein as an electronic flash and an electronic flash unit as well as an electronic flash device.
2. Description of the Prior Art
Various electronic flash devices of this kind have been proposed. In such electronic flash devices, the quantity of light reflected from a preliminary flash is integrated and the device produces signal for controlling the aperture of a camera's photo-taking lens on the basis of the integration and another signal. This serves for adjusting the light control level of the device to a level corresponding to the aperture size controlling signal. It is an advantage of the conventional devices of this kind that they adjust the aperture of the lens to a smaller size when the object is closer to the camera and hence, produce a proper exposure over a wide range up to a long distance to the object. However, a disadvantage of the conventional devices on the other hand resides in that a considerable amount of light energy is wastefully discharged even for an object located close to the camera and this inevitably results in a prolonged interval between one flash and another, or in other words, a longer recycle time.